Toggle Combobox!
<br>
<button cdkCombobox class="example-combobox" [cdkComboboxTriggerFor]="panel" [openActions]="'toggle'">
    No Value
</button>

<ng-template cdkComboboxPanel #panel="cdkComboboxPanel">
    <div cdkComboboxPopup [parentPanel]="panel" [firstFocus]="input">
        <input #input>
        <button (click)="panel.closePanel(input.value)">Apply</button>
    </div>
</ng-template>
